linux-kernel - Re: [PATCH v2 4/4] x86/resctrl: Rename arch_has_sparse

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Date:   Thu, 28 Sep 2023 13:47:49 -0700
From:   Reinette Chatre <reinette.chatre@...el.com>
To:     Maciej Wieczor-Retman <maciej.wieczor-retman@...el.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>
CC:     <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 4/4] x86/resctrl: Rename arch_has_sparse_bitmaps

Hi Maciej

Could you please move this patch to the beginning of this series?
Having it in the end results in a lot of churn with significant
changes to new code introduced in this series. All this can be avoided
by providing a smaller patch at the beginning of the series.

On 9/22/2023 1:48 AM, Maciej Wieczor-Retman wrote:
> Both AMD and Intel documentations use capacity bitmasks terminology
> rather than capacity bitmaps. Also bitmask term is much more widely
> used inside x86 resctrl code.

Since resctrl is intended to support many architectures and Arm coming
soon (and they use bitmap) I do not think we should use the vendor's
language as a motivation. For me there are three reasons supporting the
rename:
* arch_has_sparse_bitmaps is the *only* instance in resctrl that uses
  the bitmap term for capacity bitmasks, all other parts of resctrl refers
  to it as a bitmask
* bitmask is the established term used in resctrl documentation
  (Documentation/arch/x86/resctrl.rst)
* bitmask is the term already exposed to user space via resctrl ("cbm_mask")

Finally, why do the rename as part of this work? This can be motivated
with something like:
	A later patch exposes the value of arch_has_sparse_bitmaps to
	user space via the existing term of a bitmask. Rename
	arch_has_sparse_bitmaps to arch_has_sparse_bitmasks to ensure 
	consistent terminology throughout resctrl.

> 
> Unify the naming convention by renaming arch_has_sparse_bitmaps struct
> member to arch_has_sparse_bitmasks.
> 
> Suggested-by: Reinette Chatre <reinette.chatre@...el.com>
> Signed-off-by: Maciej Wieczor-Retman <maciej.wieczor-retman@...el.com>
> ---

...

> diff --git a/include/linux/resctrl.h b/include/linux/resctrl.h
> index 8334eeacfec5..83c2cbf7136d 100644
> --- a/include/linux/resctrl.h
> +++ b/include/linux/resctrl.h
> @@ -57,7 +57,7 @@ struct resctrl_staged_config {
>   * @list:		all instances of this resource
>   * @id:			unique id for this instance
>   * @cpu_mask:		which CPUs share this resource
> - * @rmid_busy_llc:	bitmap of which limbo RMIDs are above threshold
> + * @rmid_busy_llc:	bitmask of which limbo RMIDs are above threshold
>   * @mbm_total:		saved state for MBM total bandwidth
>   * @mbm_local:		saved state for MBM local bandwidth
>   * @mbm_over:		worker to periodically read MBM h/w counters

Please drop this hunk. rmid_busy_llc is indeed a bitmap.

Reinette